This invention relates to a high efficiency furnace and, in particular, to a method and apparatus for removing condensate from a high efficiency furnace.
In recent years, high efficiency furnaces have been developed which are capable of utilizing most of the energy that is available in the fuel that is burned. Typically, these furnaces contain a primary heat exchanger and a secondary heat exchanger that are mounted in series. The hot gases of combustion, herein referred to as flue gases, are passed through the heat exchangers in heat transfer relation with comfort air to efficiently heat the comfort air to a desired level. An inducer fan is connected to the flue gas exit of the secondary heat exchanger to draw the flue gases through the heat exchanger system and force the gases under pressure through the venting system of the furnace.
With furnace efficiencies in excess of 90%, any moisture contained in the flue gases will form from condensate in the gas flow as it moves from the secondary heat exchanger through the inducer fan housing into the vent system. Furnace standards require that the condensate be collected and removed from the furnace to insure that it does not harm the working parts and surfaces of the furnace.
It has been found that under the influence of the inducer fan, the velocity of the flue gases leaving the inducer fan housing are high enough to create pressures in the vent pipe such that the condensate accumulates in the vent system. The condensate builds up in the vent system and is finally released when it overcomes the holding pressure of the flue gas flow. Upon release, the condensate "slugs" back into the inducer housing. This, in turn, creates unwanted furnace noise and, under certain conditions, slows down the inducer fan causing the pressure sensor switch to drop out, shutting down the furnace. Under certain operating conditions, the condensate can build up in the vent system such that vent pressures are reduced to a level where proper venting cannot be maintained and undesirable turbulent flow conditions are created which again, produces unwanted noise.